Surely the binocular transformer is converting the input impedance of
the filter to the optimum load line for the PA transistors. Typically
that would mean such that the the voltage swing was just short of the
full supply rail for the worst case complex impedance, at the worst case
acceptable SWR, for maximum power, and with that power.
Also that transformer provides negative feedback.
I'd expect the actual PA collector impedance to be a lot higher than the
impedance reflected through the transformer, as transistors and FETs
are, to a first approximation, current sources, although the negative
feedback would actually make the reverse termination impedance much
lower than that from the transformer.
A hint that is the case is the option for different winding ratio if you
are always going to use a lower maximum power. Maximising the voltage
swing increases the efficiency. The alternative ratio doesn't transform
the filter input impedance down so much.
I mention this as there is a common misconception that the "maximum
power transfer theorem" actually applies in such cases, when applying it
would produce less than 50% efficiency.
--
David Woolley
Owner K2 06123
On 25/10/2020 18:17, Don Wilhelm wrote:
The binocular toroid is a transformer to match the impedance of the PA
collectors to 50 ohms, which is the input impedance of the Low Pass
Filters.
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